Lighting for root growth

ABSTRACT

A biological lighting system to provide temporally- and spatially-modulated photon flux output and spectral power distributions to plants on a circadian and circannual basis, or circadian and life cycle basis, to maximize effective and efficient growth in a horticultural setting. The photon flux or irradiance output and the spectral power distribution are modulated to match circadian and circannual rhythms, with individual or multiple luminaires controlled through one or more controllers. Different lighting spectra can be employed depending on the direction of illumination. The photon flux or irradiance output and the spectral power distribution may be set as best suited for any particular plant species, and the system is also useful for raising animals.

TECHNICAL FIELD

The subject matter of the present invention relates to the field ofbiological lighting systems and more particularly, is concerned withproviding temporally- and spatially-modulated spectral powerdistributions to plants and animals on a circadian basis to entraincircadian rhythms, and also on a circannual or life cycle basis.

BACKGROUND

Biologists have long known that plants and animals have both circadianand circannual rhythms, wherein their biological functions vary on adaily and annual basis. These rhythms are endogenously generated andself-sustaining, so that they persist in the absence of environmentaltime cues, or “zeitgebers.” Flowering plants are obvious examples, asmost flowers open or close at dawn and dusk. An example thatdemonstrates the self-sustaining nature of circadian rhythms is thesensitive heliotrope plant Mimosa pudica, whose leaves droop at night,even when the plant is kept in constant darkness. In animals, sleep isthe most obvious example of circadian rhythms, but there are many more,including cardiovascular efficiency, blood pressure, bowel movements,alertness, and appetite.

There are similarly many other biological functions in plants thatexhibit circadian rhythms, including leaf and flower movement, andnectar secretion (McClung, C. R., 2001, “Circadian Rhythms in Plants,”Annual Review of Plant Physiology 52:139-162). More subtly, biochemicalchanges at the cellular level occur that prepare the plants for coldertemperatures at night, regulate the opening and closing of stomata forgas exchange, anticipate possible infection by pathogens, produce wax toprevent water loss, and synthesize molecules that will remove reactiveoxygen species before sunrise and protect against excess sunlight duringthe day. Kamioka, M. et al., 2016, “Direct Repression of Evening Genesby CIRCADIAN CLOCK-ASSOCIATED 1 in the Arabidopsis Circadian Clock,” ThePlant Cell 28:696-711 demonstrated that daily gene expression oftenoccurs hours in advance, and in highly complex biochemical pathways,that control various mechanisms needed for plant health and survival.

Plants also exhibit circannual rhythms, obvious examples being the lossof leaves for deciduous trees in the autumn and annual tree ring growth.(Like mammals, reptiles, and amphibians living in colder temperatureclimates, trees and perennial plants hibernate during the wintermonths.) More subtly, flowering plants in temperate climates areinfluenced by the day length. So-called “short-day” plants flower whenthe night length (“skotoperiod”) exceeds their critical “photoperiod,”while “long-day” plants flower when the skotoperiod is less than theircritical photoperiod. (Some “day-neutral” flowering plants rely on otherenvironmental cues, such as periods of low temperature.)

Plants rely on photoreceptor proteins (“photopigments”) such asphytochromes (which are sensitive to red light) to determine the nightlength and so initiate flowering at the appropriate time (e.g., Smith,H., 2000, “Phytochromes and Light Signal Perception by Plants—AnEmerging Synthesis,” Nature 407:585-591). The roles of thesephotopigments are ascertained by breeding genetically-modified plants inwhich the genes responsible for the biosynthesis of the photopigmentsare not expressed. Floriculturists use both incandescent lamps and, morerecently, red light-emitting diodes (LEDs) to influence seedgermination, leaf development, and stem elongation, and to promote orsuppress flowering in photoperiodic plants. This is possible because therole of phytochromes has been well understood for many decades, and theplant responses are clearly evident.

Generally assuming that photopigments such as phytochromes are aloneresponsible for photoperiodic responses, horticultural research has todate focused on the photon flux delivered to plants on a daily basis.This is the basis of the “daily light integral” (DLI), which is measuredas moles of photons received per square meter in a 24-hour period.Horticulturalists have documented the daily light integrals of mosteconomically-important crops and use this information to determine thesuitability of various climatic regions for their production.(Circannual rhythms are accounted for by “growing degree-days,” a metricthat is based on ambient temperature rather than available daylight.)

The daily light integral as a metric for predicting plant growth is,however, perhaps overly simplistic. As described by Blanchard, M. G. andE. S. Runkle, 2016, “Investigating Reciprocity of Intensity and Durationof Photoperiodic Lighting to Regulate Flowering of Long-Day Plants,”Acta Horticulturae 1134:41-48, the relationship between the photon fluxdensity at the plant canopy (measured in micromoles per square meter persecond, or μmol/m²-sec) and the duty factor of the cyclic exposure(e.g., 2 minutes every 45 minutes versus continuous exposure) is notnecessarily linear—it depends on the plant species.

Central then to both the circadian and circannual rhythms of plants isthe reliable functioning of the endogenous circadian clocks. Withoutdaily environmental cues, the free-running circadian clock periods aretypically less than 24 hours (McClung 2001.) As shown by Dodd, A. N., etal., 2005, “Plant Circadian Clocks Increase Photosynthesis, Growth,Survival, and Competitive Advantage,” Science 309:630-633, plants withentrained circadian rhythms contain more chlorophyll, fix more carbon,grow faster, and survive better. Similarly, many studies have shown thatcircadian rhythm disruption in animals—“jet lag” in humans is a goodexample—negatively impact the animals' long-term health and well-being.It is important then to understand the environmental cues that serve toentrain both circadian and circannual rhythms to their daily and annualperiods respectively.

Circadian Rhythm Entrainment

In Walmsley, L., et al., 2015, “Colour as a Signal for Entraining theMammalian Circadian Clock,” PLOS Biology 13(4):e1002127, the researchersinvestigated the entrainment of circadian and circannual rhythms in wildmice. They noted that daylight irradiance may not be the most reliablezeitgeber for entraining their circadian and circannual rhythms. Inparticular, the daylight irradiance may vary markedly and rapidly fromminute to minute and day to day, depending on the cloud cover. Theaverage daylight colour, however, is remarkably constant from day today. (As noted in Lee, R. L., and J. Hernández-Andrés, 2006, “Colour ofthe Daytime Overcast Sky,” Applied Optics 44(27):5712-5722, cloudsdiffuse daylight, but rarely change its average colour, expressed ascorrelated colour temperature. The colour further varies only slowlythroughout most of the day, apart from dawn and dusk.) As reported byWalmsley et al. (2015), the ratio of yellow to blue light, or what theyrefer to as “relative colour,” varies much less than daylight irradiance(FIG. 1). They demonstrated that, at least for wild mice, circadianrhythm entrainment is most likely due to changes in the average skycolour at dawn and dusk, rather than changes in daylight irradiance.

Walmsley et al. (2015) also reported that the ratio of yellow to bluelight consistently varies by a factor of three over a period of 30minutes at dawn and dusk, regardless of whether the sky condition isclear or overcast (FIG. 2). Brown, T. M., 2016, “Using Light to Tell theTime of Day: Sensory Coding in the Mammalian Circadian Visual Network,”Journal of Experimental Biology 219:1779-1792, similarly reported markedchanges in the spectral power distribution of daylight between a solarinclination of six degrees before and after sunset (FIG. 3).

Brown (2016) further noted that fish, reptiles, and possibly birds havethe ability to distinguish colour with their pineal and parietal organs.Even some plankton, such as dinoflagellates, rely on colour to entraintheir circadian rhythms, using rhodopsin, chlorophyll, and anotherunknown photopigment (Roenneberg, R., and R. G. Foster., 1997, “TwilightTimes: Light and the Circadian Rhythms,” Photochemistry and Photobiology66(5):549-562).

Another example was reported by Sweeney, A. M. et al., 2011, “TwilightSpectral Dynamics and the Coral Reef Invertebrate Spawning Response,”Journal of Experimental Biology 214:770-777, wherein the circannualsynchronized spawning of corals is determined primarily by shifts intwilight colour and irradiance on nights immediately before and afterthe full moon.

Given these examples and more (e.g., Brown 2016), it is evident thatchanges in daylight colour during twilight are an important zeitgeberfor entraining both circadian and circannual rhythms across the animalkingdom.

Data Fusion

Data fusion is the process of integrating multiple data sources toproduce more consistent, accurate, and useful information than thatprovided by any individual data source. While Walmsley et al. (2015)concluded that wild mice use daylight colour rather than irradiance toentrain their circadian rhythms, it is more likely that the mice insteadcombine the two input signals, as shown in FIG. 1. In terms ofphase-locked loop design (wherein circadian rhythms are seen asbiological oscillators—see Rascher, U. et al., 2001, “SpatiotemporalVariation of Metabolism in a Plant Circadian Rhythm: The BiologicalClock as an Assembly of Coupled Individual Oscillators,” PNAS98(20):11801-11805), a sudden but consistent periodic pulse at dawn anddusk is better for entrainment than a randomly variable and noisy signalsuch as varying daylight irradiance.

Brown (2016) and others have further reported that animals use a“temporal gating mechanism” for photoreceptors, wherein the response toinputs from non-imaging photoreceptors (intrinsically photosensitiveretinal ganglion cells, or ipRGCs, in the human retina) varies dependingon the time of day. The purpose of this gating mechanism appears to beto maximize sensitivity to changes in both daylight colour andirradiance at sunrise and sunset, while ignoring such changes during theday. In other words, the input signals are temporally preconditioned tomaximize their usefulness in synchronizing the phase-lock loopperformance of the circadian clocks.

Plants appear to have a similar gating mechanism, wherein they aresensitive to changes in red light at sunset and blue light at sunrise(e.g., Hanyu, H., and K. Shoji, 2002, “Acceleration of Growth in Spinachby Short-term Exposure to Red and Blue Light at the Beginning and at theEnd of the Daily Dark Period,” Acta Horticulturae 580:145-150 andOhashi-Kaneko, et al., 2010, “Low-light Irradiation at the Beginning orthe End of the Daily Dark Period Accelerates Leaf Expansion and Growthin Spinacia oleracea L.”, Environmental Control in Biology48(4):161-173).

It is further well known that plants synchronize their circadian clocksin response changes in the ratio of red to far-red light (R:FR) at theend of the day (e.g., Demotes-Mainard, S., et al., 2016, “PlantResponses to Red and Far-red Light, Applications in Horticulture,”Environmental and Experimental Botany 121:4-21). The R:FR ratio ofdirect sunlight is about 1.3 during most of the day, but it approaches0.6 or so during twilight. Each phytochrome molecule has two statescalled “isoforms.” Left in the dark for several hours, it reverts to astate called P_(r), where it strongly absorbs red light. If aphytochrome molecule in this state absorbs a red photon, it changes toits P_(fr) state, where it absorbs far-red radiation. If the moleculeabsorbs a far-red photon, it reverts back to its P_(r) state. When inits P_(fr) state, the molecule is biologically active, and may interactwith the plant's molecular machinery. Given this, phytochrome can beseen as a reversible biological switch that can enable or inhibitvarious plant functions. The R:FR ratio is thus another circadianzeitgeber, one that is commonly used by floriculturists to advance ordelay flowering by irradiating the plants at night (“night lighting”) todisrupt their circadian rhythms.

As might be expected with phase-lock loops, electric light pulsespresented to animals shortly before dawn may advance the circadian clockphase, while electric light pulses shortly after dusk may delay theclock phase. If the biological clock's intrinsic period is shorter than24 hours, the animal will primarily use dusk light for entrainment. If,on the other hand, the intrinsic period is longer than 24 hours, theanimal will primarily use dawn light for entrainment.

Referring to plants, McClung (2001) noted that plants use both light andtemperature as input signals for circadian rhythm entrainment, andlikely perform data fusion on these signals to obtain a statisticallymore significant entrainment signal for circadian and circannualrhythms. Although not discussed by McClung or others, annually-varyingenvironmental conditions such as soil moisture content, soil acidity,salt content, nutrient availability, carbon dioxide concentration (inenclosed greenhouses and vertical farms), and wind may also be involvedin circannual rhythm entrainment.

Plant Photoreceptors

Plants cannot, of course, “see” colour in the sense that animals, andparticularly mammals, can. The human visual system, for example, relieson opsins, including rhodopsin, melanopsin, and possibly neuropsin(Brown 2016), with colour vision conferred by the opsins OPN1LW, OPN1MW,and OPN1SW (e.g., Terakita, A., 2005, “The Opsins,” Genome Biology6:213). Wild mice have similar but not identical opsins that aresensitive to yellow light and ultraviolet radiation (Walmsley et al.2015).

While plants may not “see” in the sense of visual images, they arenonetheless capable of sensing the colour of daylight and electriclighting due to the spectral absorbance characteristics of various knownclasses of plant photoreceptors (e.g., Briggs, W. R., and M. A. Olney,2001, “Photoreceptors in Plant Photomorphogensis to Date. FivePhytochromes, Two Cryptochromes, One Phototropin, and One Superchrome,”Plant Physiology 125:85-88): phytochromes (red light), cryptochromes(blue light), phototropins (blue light), UVR8 (ultraviolet radiation),and cryptochromes (blue light). Thus, while plants may not see colour inany visual sense, they are certainly capable of sensing differences inthe spectral power distribution of daylight and electric lighting thatwe may perceive as different colours.

Infrared Radiation

As noted in ASABE, 2016, “ANSI/ASABE S640: Quantities and Units ofElectromagnetic Radiation for Plants (Photosynthetic Organisms),”American Society of Agricultural and Biological Engineers and elsewhere,the spectral wavelengths that plant photoreceptors are capable ofsensing range from 280 nm (ultraviolet-B radiation) to 800 nm (far-redlight). However, as reported by Johnson, C. F. et al., 1996, “InfraredLight-emitting Diode Radiation Causes Gravitropic and MorphologicalEffects in Dark-Grown Oat Seedlings,” Photochemistry and Photobiology63(2):238-242, plants also appear to be capable of sensing andresponding to near-infrared radiation at approximately 880 nm and 935nm.

A possible photoreceptor for near-infrared radiation is cytochrome coxidase, which is a protein complex found in the mitochondria of alleukaryotes. It is a terminal enzyme of the respiratory chain, regulatingthe transfer of electrons from cytochrome to molecular oxygen. Asreported by Karu, T., 2010, “Multiple Roles of Cytochrome c Oxidase inMammalian Cells Under Action of Red and IR-A Radiation,” Life62(8):607-610, cytochrome C in mammalian cells has a peak in its actionspectrum at 825 nm. By coincidence, the high-pressure sodium (HPS) lampsoften used for supplemental electric lighting in greenhouses and poultryfarms have a strong spectral peak at 820 nm (FIG. 4).

Karu (2010) discusses the effects of near-infrared radiation (IR-A) onmammalian, and in particularly human, cells. He notes in particular thatexposure to IR-A radiation at sunrise may precondition dermalfibroblasts against damage by exposure to ultraviolet radiation duringthe day. While this cannot be regarded as definitive evidence forplants, cytochrome c oxidase is nonetheless present in the mitochondriaof all plants (e.g., Dahan, J., et al., 2014, “Disruption of theCYTOCHROME C OXIDASE DEFICIENT1 Gene Leads to Cytochrome c OxidaseDepletion and Reorchestrated Respiratory Metabolism in Arabidopsis,”Plant Physiology 166:1788-1802).

This is important because as reported by Poyton, R. O. and K. A. Ball,2011, “Therapeutic Photobiomodulation: Nitric Oxide and a Novel Functionof Mitochondrial Cytochrome C Oxidase,” Discovery Medicine11(57):154-159, exposure to low-level intensity light (albeit at 590 nmfor human subjects) enhances nitric oxide (NO) synthesis by cytochrome coxidase without altering its ability to reduce oxygen. Nitric oxide,according to Rio, L. A. et al., 2004, “Nitric Oxide and Nitric OxideSynthase Activity in Plants,” Phytochemistry 65:783-792, functions as anintracellular and intercellular signaling molecule in plants. Asreported by Beligni, M. V. and L. Lamattina, 2001, “Nitric Oxide inPlants: The History is Just Beginning,” Plant, Cell and Environment24:267-278, exogenously-applied NO results in increased leaf expansionrates, stem and root elongation, delayed senescence, accelerated seedgermination, and increased post-harvest life of flowers, fruits, andvegetables.

Anecdotal reports from horticulturalists have indicated that cucumbers,tomatoes, and gerbera (African daisies) do not grow as well underLED-based lighting as they do under HPS lighting, even with comparablephotosynthetically active radiation (PAR) values. It is thereforeproposed that the difference is the lack of 820 nm radiation withLED-based lighting, and that horticultural luminaires equipped withnear-infrared LEDs with peak wavelengths between approximately 800 nmand 1000 nm, and which provide irradiance levels comparable to HPSlighting, will result in better plant health and growth.

It is also possible, based on the evidence of the response of human skinto near-infrared radiation at dawn to precondition the skin againstultraviolet radiation damage later in the day (Karu 2010), that asimilar cellular mechanism exists in plants, which are also susceptibleto ultraviolet radiation damage of their leaves, stems, and flowers. Assuch, horticultural luminaires equipped with near-infrared LEDs withpeak wavelengths would provide benefits to plants grown in greenhouseswith supplemental lighting.

Directionality Sensing

It has been hypothesized that plants may be able to image theirenvironment using ocelli, or photosensitive “eye spots.” Baluška, F.,and S. Mancuso, 2016, “Vision in Plants via Plant-Specific Ocelli?”,Trends in Plant Science 21(9):727-730, for example, noted that the upperepidermal cells of many leaves are shaped like convex or planoconvexlenses, which in turn are capable of focusing light on thephotosensitive subepidermal cells. This hypothesis was recentlysupported by Crepy, M. A. et al., 2015, “Photoreceptor-mediated KinRecognition in Plants,” New Phytologist 205:329-338, wherein Arabidopsisthalania plants were shown to visually recognize plant kin and modifytheir growth accordingly.

Further evidence in support of this hypothesis comes from Hayakawa, S.et al., 2015, “Function and Evolutionary Origin of UnicellularCamera-Type Eye Structure,” PLoS One 10(3):e0228415, who reported thatocelloids in the dinoflagellate family Warnowiacease function asprimitive eyes, enabling the plankton to sense and swim towards daylightin order to maximize photosynthesis opportunities. Schuergers, N. etal., 2016, “Cyanobacteria Use Micro-optics to Sense Light Direction,”eLife 5:e12620 reported similar capabilities for even simpler lifeforms, suggesting that primitive vision capabilities are not limited toanimals.

While apparently not considered in the literature, it is possible thatplant leaves may function as compound lenses similar to those evolved byinsects and crustaceans. Given that most leaves move in the wind, anyperceived image would have very low resolution. However, this may besufficient to determine, for example, the directionality of directsunlight or the spatial distribution of sky colour at sunrise andsunset. (An example of this from the animal kingdom is presented inSumner-Rooney, L. et al., 2018, “Whole-body Photoreceptor Networks areIndependent of ‘Lenses’ in Brittle Stars,” Proc. Royal Society B285(1871), wherein photoreceptor cells embedded in skin across theentire body of brittle stars enables them to perceive distant shadowsand so avoid potential predators.)

The sky colour on clear days near sunrise and sunset is typicallydifferent than the average sky colour, due to Rayleigh scattering ofblue light and ozone absorption of red light by the atmosphere (e.g.,Hulburt, E. O., 1953, “Explanation of the Brightness and Colour of theSky, Particularly the Twilight Sky,” Journal of the Optical Society ofAmerica 43(2):113-118). More important, however, is the spatialdifference in sky colour at sunset and twilight, varying from yellow andred near the horizon to blue at zenith. It is therefore reasonable tohypothesize that plants perceive the directionality of red and bluelight at dawn and dusk and use data fusion to extract a more reliablezeitgeber for circadian rhythm entrainment than relying on daylightcolour and irradiance alone.

It is also possible that rather than relying on putative ocelli, plantsperceive changes in red light using red-sensitive phytochromes andchanges in blue light using blue-sensitive cryptochromes and/orphototropins. As reported by Liscum et al., 2014, “Phototropism: GrowingTowards an Understanding of Plant Movement,” The Plant Cell 26:38-55,plants such as sunflowers follow the path of the sun during the dayusing phototropins phot1 and phot2, which signal stem cells to grow andso turn the flowers in the direction of the sun. It is known that thesephotoreceptors mediate a number of other plant functions in response toblue light, including stomatal opening, photosynthetic gas exchange, aswell as cotyledon and leaf blade expansion, flattening, and positioning.It is therefore reasonable to assume that the phototropin signals (andpossibly those from cryptochromes) would be used with the phytochromesignals for data fusion.

Whatever the underlying mechanism, plants appear to be capable ofsensing the spatial and temporal distribution of both the spectral powerdistribution (i.e., colour) and irradiance of daylight across the skydome at dawn and dusk. (It is also conceivable that plants may be ableto sense the polarization of daylight.) This suggests at least eightco-dependent zeitgebers: the vertical distribution of colour andirradiance from horizon to zenith, the horizontal distribution of colourand irradiance from the solar to antisolar positions, and their temporalchanges, that may be combined using data fusion. As proposed by forexample Trewavas, A., 2003, “Aspects of Plant Intelligence,” Annals ofBotany 92:1-20, such capabilities may be reasonably expected of higherplants.

Root Growth

As reported by Mo, M. et al., 2015, “How and Why Do Root Apices SenseLight Under the Soil Surface?”, Frontiers in Plant Science Vol. 6, Art.775, plant roots have photoreceptors that sense daylight penetrating upto several millimeters below the surface. These photoreceptors includeUVR8, cryptochromes, phototropins, and phytochromes, even though red andfar-red light penetrates more deeply than blue light and ultravioletradiation.

Christiaens, A. et al., 2016, “Light Quality and Adventitious Rooting: AMini-Review,” Acta Horticulturae 1134:385-394, surveyed 18 papers ontrial-and-error studies of in vitro plant cultures to determine theeffects of broadband and quasimonochromatic visible light on rootgrowth. Other studies have elucidated the role of red and far-red light(e.g., Correll, M. J., et al., 2005, “The Role of Phytochromes inElongation and Gravitropism of Roots,” Plant Cell Physiology46(2):317-323) and blue light (e.g., Kutschera, U., et al., 2012, “RootPhototropism: From Dogma to the Mechanism of Blue Light Perception,”Planta 235:443-452) in terms of photoreceptors and auxin signaling butdid not consider the in vivo responses of plants in the field to naturaldaylight.

In addition to sensing scattered light within the soil, Lee, H.-J. etal., 2106, “Stem-piped Light Activates Phytochrome B to Trigger LightResponses in Arabidopsis thalania Roots,” Science Signalling9(452):ra106, demonstrated that ambient light incident upon plant leavesand stems is transmitted to the roots via vascular bundles. Thephotoreceptors in the roots are therefore potentially responsive todaylight colour changes, including those at dawn and dusk.

As reported in a survey by Satbhai, S. et al., 2015, “UndergroundTuning: Quantitative Regulation of Root Growth,” Journal of ExperimentalBotany 66(4):1099-1112, the spectral power distribution of above-groundirradiation can influence root growth rate, branching, and hair density,which may be particularly important when plants are cloned fromcuttings. As noted by Christiaens et al. (2016), however, the optimalspectral power distribution for root development may be suboptimal forabove-ground shoot growth, and vice versa.

US Patent Application Pub. No. 2018/0054974 discloses the use ofnear-infrared lighting to promote growth and production of various cropplants, where the leaves, stems, and flowers of the plants are exposedto a combination of photosynthetically active radiation andnear-infrared radiation. However, much of the intelligence of plants isdevoted to the behaviour of root tips in efficiently locating water andmineral resources in the soil, and so the root system benefits the mostfrom effective intercellular communications. Near-infrared radiationresults in increased production of nitric oxide by cytochrome c oxidase(Poyton et al. 2011), and near-infrared radiation penetrates more deeplyinto soil compared to visible light. Irradiating plant root systems withnear-infrared radiation may therefore benefit plant health and growth.

Silva-Nava, J. et al., 2015, “D-Root: A System for Cultivating Plantswith the Roots in Darkness or Under Different Light Conditions,” ThePlant Journal 84:244-255, disclosed an apparatus (Spanish patent ES1091883Y) for irradiating plant root systems with LEDs or UV-B lampsindependently of above-ground irradiance, but it is practical only forresearch purposes using controlled growth chambers. There is therefore aneed for an apparatus that provides mostly independent control ofabove-ground and below-ground irradiation of plants.

Solid State Lighting

The advent of solid-state lighting, in particular the availability ofhigh-flux semiconductor LEDs with narrow spectral bandwidths that spanthe photobiologically-active spectrum from approximately 280 nm to 800nm and beyond, makes it possible to design and manufacture horticulturalluminaires with precisely-controlled spectral power distributions.However, research to date has been either trial-and-error with nounderlying hypothesis (e.g., Johkan, M., et al., 2012, “Effect of GreenLight Wavelength and Intensity on Photomorphogenesis and Photosynthesisin Lactuca sativa,” Environmental and Experimental Botany 75:128-133),or the reductionist approach of observing the effects of genome editingof single plant species such as Arabidopsis.

Companies such as Fluence Bioengineering (Austin, Tex.) and Lumigrow(Emeryville, Calif.) manufacture horticultural luminaires with variablespectral power distributions, which can be preset according to whetherthe horticulturalist or floriculturist is interested in propagatingseedlings or cuttings, promoting vegetative growth, or flowering.Similarly, companies such as Once Innovations (Plymouth, Minn.)manufacture livestock production luminaires for chicken, turkey andswine facilities, and aquaculture luminaires for fish farming Chickens,for example, may be exposed to red light during brooding to promoteearly growth and blue light for improved feed conversion ratios,improved bird behaviour, and other desired productivity goals (Delabbio,J. L. 2018. “The Science of Poultry Lighting,” Plymouth, Minn.: OnceInnovations Inc.).

SUMMARY

The present invention emulates changes in sky colour, sky colourdistribution and sky irradiance to influence plant health, growth, andthe production of flavonoids and other medicinally useful plant extractsthrough circadian and circannual rhythm entrainment. The invention alsoemulates changes in sky colour, colour distribution and irradiance toinfluence animal health and growth through circadian and circannualrhythm entrainment.

In order to promote the health and well-being of both plants andanimals, the inventors have recognized a need for a biological luminaireand control system with a temporally and spatially varying spectralpower distribution that can be optimized for specific plant speciesgrown in greenhouse or vertical farm environments, or specificfactory-raised animal species, such that the temporal and spatialchanges in spectral power distribution serve to beneficially entraintheir circadian and circannual rhythms or, for animals that live lessthan a year, their circadian and life cycle rhythms.

In a first embodiment, the invention includes a colour-changingluminaire with an associated controller that adjusts the spectral powerdistribution and photon or radiant flux output of the luminaire toemulate the colour and irradiance changes of daylight for the purpose ofentraining circadian rhythms and either circannual or life cyclerhythms.

In a second embodiment, the invention includes at least twocolour-changing luminaires with an associated controller that adjuststhe spectral power distribution and photon or radiant flux output of theluminaires to emulate the spatial and temporal changes in daylightcolour and irradiance for the purpose of entraining circadian rhythmsand either circannual or life cycle rhythms.

In a third embodiment, the invention includes at least twocolour-changing horticultural luminaires with an associated controllerthat adjusts the spectral power distribution and photon flux output toemulate the colour and irradiance changes of daylight for the purpose ofentraining circadian rhythms and either circannual or life cycle rhythmsand promoting plant health and growth, wherein at least one luminaireprovides above-ground irradiation to the plant stems, shoots, leaves,and flowers, and at least one luminaire provides below-groundirradiation to the plant root system.

Disclosed herein is an illumination system comprising a luminaire havingan adjustable spectral power distribution (SPD) and a controller thatprovides electrical power and control signals to the luminaire. Thecontrol signals automatically transition the SPD between a first SPD anda second SPD, wherein the transition corresponds to a change in lightthat entrains a biological rhythm in a life form.

Further disclosed is method for entraining a biological rhythm in a lifeform comprising the steps of: orienting a luminaire with an adjustablespectral power distribution (SPD) to illuminate the life form fromabove; connecting a controller to the luminaire so that the controllerprovides electrical power and control signals to the luminaire; andsending, automatically from the controller, control signals thattransition the SPD between a first SPD and a second SPD; wherein thetransition corresponds to a change in light that entrains a biologicalrhythm in the life form.

The disclosed and/or claimed subject matter is not limited by thissummary, as additional aspects are presented by the following writtendescription and associated drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a prior art graph that shows daylight colour versus irradiancevariability.

FIG. 2 is a prior art graph that shows the variation in yellow-bluedaylight ratio at dawn and dusk.

FIG. 3 is a prior art graph that shows daylight SPD before and aftersunset.

FIG. 4 is a prior art graph that shows the SPD of a typicalhigh-pressure sodium (HPS) lamp commonly used for supplemental electriclighting in greenhouses and poultry farms.

FIG. 5 shows a first embodiment of a plant illumination system thatincludes spectral and temporal control.

FIG. 6 shows a second embodiment of a plant illumination system thatincludes spectral, spatial, and temporal control.

FIG. 7 shows a third embodiment of a plant illumination system thatincludes spectral, spatial, and temporal control.

FIG. 8 shows a flowchart for the optimization of temporally- andspatially-varying SPD for optimal plant health and growth, according toan embodiment of the present invention.

FIG. 9 shows a flowchart for the optimization of temporally- andspatially-varying SPD for optimal animal health and growth, according toan embodiment of the present invention.

FIG. 10 is a flowchart of a process for transitioning the SPD, accordingto an embodiment of the present invention.

FIG. 11 is a flowchart of a process for transitioning the distributionof illumination, according to an embodiment of the present invention.

DETAILED DESCRIPTION

Glossary

Dawn—the period of time wherein the geometric centre of the sun iswithin 6 degrees above or 8 degrees below the horizon in the morning,for a given geographic location.

Dusk—the period of time wherein the geometric centre of the sun iswithin 6 degrees above or 8 degrees below the horizon in the evening,for a given geographic location.

R:FR—The ratio of red light to far-red light in a spectral powerdistribution

SPD—Spectral power distribution

Twilight—The soft, diffused light from the sky when the sun is below thehorizon, either from daybreak to sunrise or, more commonly, from sunsetto nightfall. In particular, twilight herein refers to the sky'sspectral power distribution and irradiance when the sun is not visibleabove the horizon and its geometric centre is within 8 degrees below thehorizon.

Exemplary System

In FIG. 5, a plant illumination system 500 is shown for plants 510growing in or from a substrate 520, wherein the substrate is soil or asupport structure for hydroponic or aeroponic agriculture depending onthe embodiment. The system 500 includes one or more horticulturalluminaires 530 providing substantially directional or omnidirectionalillumination 540 to the plants, and in some embodiments the substrate520 forms part of the system. In this example, the light 540 from theluminaires 530 illuminates the plants 510 from above, providing theillumination at least in a vertical or downwards direction. The photonflux output and SPD of luminaires 530 are adjustable and are controlledby luminaire controller 550, which provides electrical power and controlsignals to the luminaires.

One or more sensors 560, such as for example a computer vision system ora chlorophyll fluorescence sensor (e.g., Lindqvist, J., et al., 2016,“Complexity of Chlorophyll Fluorescence Dynamic Response as an Indicatorof Expressive Light Intensity,” IFAC-PapersOnline 49-16:392-397) isemployed in some embodiments to monitor plant status and providefeedback to controller 550. In some embodiments, one or more sensors570, such as for example a quantum sensor, colorimeter, a soiltemperature sensor, a soil moisture sensor, a soil acidity sensor, anair temperature sensor, a carbon dioxide concentration sensor, or ananemometer, is employed to monitor environmental conditions and providefeedback to controller 550. In designing control systems forhorticultural, livestock production, and aquaculture lighting, it isuseful to consider all possible circadian zeitgebers, including at leastdaylight colour and irradiance, and ambient temperature, and how theplants or animals might perform data fusion of the inputs in respondingto them.

The controller 550 includes one or more interfaces via which theluminaires 530 are connected, and one or more interfaces via which thesensors 560, 570 are connected The controller has a processor, which mayinclude multiple constituent processors, that is connected to theinterfaces and to one or more computer-readable memories storing aprogram in the form of computer-readable instructions, which, whenexecuted by the processor, cause the controller to automaticallytransition the SPD of the luminaires 530 from one SPD to another. Thememory also stores computer-readable data, which is used by theprocessor to run the program. The data is created by the program, by anexternal program, or both. The data includes the times of sunset andsunrise for an optimal latitude for growth of the plants, desired SPDsfor illumination from above, the side or omnidirectional SPD, SPDtransitions, and durations of the SPD transitions, some or all of whichentrain a biological rhythm of the plants. In some embodiments, the dataincludes the condition or status of the plants in response to theillumination that has been or is being provided to the plants.

In operation, controller 550 is programmed to control the photon fluxoutput and SPD of luminaires 530 such that the illumination colour andirradiance changes at the beginning and end of the daily illuminationperiod with the intent of optimally entraining the plants' circadian andcircannual rhythms. The beginning of the daily illumination periodcorresponds, for example, to the start of dawn for the geographiclocation in which the plants are preferably grown, and the changes inillumination are made over the duration of this dawn. The end of thedaily illumination period corresponds, for example, to the end of duskfor the geographic location in which the plants are preferably grown,and the changes in illumination are made over the duration of this dusk.

Controller 550 may optionally perform data fusion of the inputs fromsensors 560 and 570 by first preconditioning the signals, as for exampleby temporal gating of a quantum sensor, and then performing data fusionoperations that emulate the plant responses to environmental conditions.For example, if luminaires 530 provide supplemental electricillumination in a greenhouse, the controller may choose, on an overcastday, to augment the colour and irradiance changes perceived by theplants at sunrise or sunset such that it appears to the plants to be aclear day with a less ambiguous entrainment signal.

If there is no other lighting on the plants other than that provided bythe luminaires 530, the output of the luminaires transitions between anSPD that alone emulates daylight and an SPD that alone emulatestwilight. In particular, the output of the luminaires varies between anoutput that emulates the sky colour and irradiance when the geometriccentre of the sun is 6 degrees above the horizon, and an output thatemulates the sky colour and irradiance when the geometric centre of thesun is 8 degrees below the horizon (i.e., the luminaires emulatetransitions spanning the “golden hour” and “blue hour”). Depending onthe embodiment, the output of the luminaires varies gradually, in stepsor abruptly, or varies between outputs that emulate the sky colour andirradiance for sun inclinations that are within than 6 degrees above to8 degrees below the horizon for the particular geographic location orlatitude of interest. However, if the luminaires 530 provide lighting inaddition to natural lighting, the output of the luminaires transitionsbetween an SPD that in combination with the natural lighting emulatesdaylight and an SPD that in combination with the natural lightingemulates twilight.

In one embodiment, the illumination colour changes emulate the changesthat are observed in nature during twilight. In another embodiment, theillumination colour changes are chosen such that the plantphotoreceptors optimally respond. It is known, for example, thatphytochrome isoforms P_(r) and P_(fr) have specific peak spectralabsorptances that differ from the SPD of natural illumination at andnear twilight. Floriculturists sometimes use black shades at sunset toprevent the flowering crops from responding to changes in the R:FRratio, but the same result can be achieved without mechanical shades byproviding supplemental red or far-red lighting with quasimonochromaticLEDs with peak wavelengths close to the photoreceptor peak spectralabsorptances to counteract or reinforce changes in the R:FR ratio atdusk. Similarly, supplemental red or blue lighting may be provided bythe luminaires 530 at dawn to counteract or reinforce the responses tonatural blue light. Supplemental red, far-red, and/or blue light mayalso be provided by the luminaires 530 before dawn or after dusk toadvance or delay the plants' circadian clocks. The luminaires 530 inanother embodiment further include near-infrared light-emitting diodeswith peak wavelengths between approximately 800 nm and 1000 nm, andpreferably near the spectral peak at 820 nm for cytochrome c oxidaseactivation. Such LEDs are activated at dawn to precondition the plantleaves, stems, shoots, and flowers against ultraviolet radiation damagefrom direct sunlight. (This applies even for indoor vertical farms,where it is becoming increasingly economical to provide ultravioletradiation from UV-B and UV-A light-emitting diodes in order to promotethe production of flavonoids and medicinal compounds.)

FIG. 5 may also represent a livestock production or aquaculture facilitywhere luminaires 530 provide lighting for captive animals (not shown)and environmental sensors 570 such as, for example, air temperaturesensors, provide input signals to controller 550, which is programmed tocontrol the radiant output and SPD of luminaires 530 such that theillumination colour and irradiance changes at the beginning and end ofthe daily illumination period with the intent of optimally entrainingthe animals' circadian and circannual rhythms. Depending on theembodiment, substrate 520 may be omitted or may represent a barn flooror fish pond, for example Animals may reside in or on the substrate, atleast part of the time.

Controller 550 may further be configured such the daily photoperiod isvaried according to the seasons experienced by wild plants or animals.For plants and animals from temperate and arctic climates, thetransition times at dawn and dusk can be similarly varied, being longerin winter months than summer months.

For the purposes of livestock production and facilities and aquaculturefarms, the controller 550 may further provide excess blue light in itstransition at dawn for animals with long-period circadian clocks, orexcess red light or far-red in its transition at dusk for animals withshort-period circadian clocks.

FIG. 6 shows a plant illumination system 600 for plants 610 growing inor from a substrate 620. The system 600 includes one or morehorticultural luminaires 630 providing substantially omnidirectionalillumination 640 to the plants 610. As above, the substrate forms partof the system 600 in some embodiments. The photon flux output and SPD ofluminaires 630 are adjustable and are controlled by luminaire controller650, which provides electrical power and control signals to theluminaires. In addition, further horticultural luminaires 660 providesubstantially directional illumination 670 that is also controlled byluminaire controller 650. The further luminaires 660 provideillumination in a sideways or horizontal direction to the plants 610.Further, one or more sensors 680, are employed in some embodiments tomonitor plant status and environmental conditions and provide feedbackto controller 650.

In operation, controller 650 is programmed to control the photon fluxoutput and SPD of luminaires 630 and 660 such that the illuminationcolour changes at the beginning and end of the daily illumination periodwith the intent of optimally entraining the plants' circadian andcircannual rhythms. The operation of controller 650 is the same as thatof controller 550 in FIG. 5, with the addition that the photon fluxoutputs and SPDs of luminaires 630 and 660 may differ in order toemulate the temporal and spatial distributions of daylight colour (orSPD) and irradiance at dawn and dusk.

FIG. 6 may also represent a livestock production or aquaculture facilitywhere luminaires 630 provide lighting for captive animals (not shown)and environmental sensors 680 such as, for example, air temperaturesensors, provide input signals to controller 650, which is programmed tocontrol the radiant output and SPD of luminaires 630, 660 such that theillumination colour and irradiance changes at the beginning and end ofthe daily illumination period with the intent of optimally entrainingthe animals' circadian and circannual rhythms. As above, the substrate620 may be omitted or may represent a barn floor or fish pond, forexample. Animals may reside in or on the substrate, at least part of thetime.

FIG. 7 shows a plant illumination system 700 for plants 710 growing inor from a substrate 720. The system 700 includes the substrate 720, andone or more horticultural luminaires 730 providing substantiallydirectional or omnidirectional illumination 740. In this example, thelight 740 from the luminaires 730 illuminates the plants 710 from above,providing the illumination at least in a vertical or downwardsdirection. The photon flux output and SPD of luminaires 730 areadjustable and are controlled by luminaire controller 750, whichprovides electrical power and control signals to the luminaires. Inaddition, horticultural luminaires 760 provide illumination directly tothe substrate 720 and have a photon flux output and SPD that are alsocontrolled by luminaire controller 750.

For soil substrates, the illumination from horticultural luminaires 760may be provided, for example, by a fiber-optic mesh 770 embedded in thesubstrate, wherein the fiber-optic strands are designed to emit lightalong their length. Light from the luminaires 760 is directed into themesh 770 by relatively lossless optic fibers 780 or other light guides.An example of such a fiber optic is disclosed in Shustack, P. J. et al.,2014, “Photocuring in Areas Where You Typically Cannot Get Light,” Proc.UV+EB Technology Expo and Conference 2014.

For hydroponic and aeroponic applications, the horticultural luminaires760 may illuminate a fiber-optic mesh 770, or they may directlyilluminate the plant roots through a transparent growth medium in orforming part of the substrate 720.

In operation, controller 750 is programmed to control the photon fluxoutput and SPD of luminaires 730 such that the illumination colour andirradiance changes at the beginning and end of the daily illuminationperiod with the intent of optimally entraining the plants' circadian andcircannual rhythms. Controller 750 may also be programmed to control thephoton flux output and SPD of luminaires 760 such that optimal rootsystem development and plant health is obtained.

Plant roots may exhibit positive phototropism for red light and negativephototropism for blue light, presumably to ensure that the roots growdownwards toward soil resources than towards the surface. One or morehorizontal layers of fiber-optic mesh, each with its own luminaire 760providing independently-controlled SPDs, may be employed in order todirect root growth and development as desired as the roots grow towardsand through the meshes.

The operation of controller 750 is the same as that of controller 550 inFIG. 5 or controller 650 in FIG. 6, with the addition that the photonflux outputs and SPDs of luminaires 730 and 760 may differ in order tooptimize root system growth independently of the above-ground plantleaves, stems, shoots, and flowers.

Plant Optimization Method

FIG. 8 illustrates an example of the method wherein the scheduling ofthe photon flux output and SPD of the luminaires is optimized for planthealth, growth, and the production of flavonoids and other medicinallyuseful plant extracts on a per-species basis.

In Step 800, a plant species is selected. It is known that differentcultivars of the same plant species may have different environmentalrequirements, and so a particular cultivar may also have to be selected.

In Step 810, the plant's preferred environmental conditions aredetermined, including geographic latitude, daily light integral andshade requirements, temperature range, soil type, moisture content,mineral nutrients, and so forth as may be present in the wild state ofthe selected plant species.

In Step 820, a baseline illumination schedule is determined based on theselected plant's preferred geographic latitude and climatic data. Thebaseline illumination schedule is intended for predetermined growthgoals of the plants to be reached. For example, if a leafy greenvegetable such as lettuce is known to thrive outdoors in a givengeographic region, a Typical Meteorological Year (TMY) weather file thatis representative of the region may be selected. The data contained inthis weather file can be used to determine sunrise and sunset, hourlytemperature, rainfall, and solar irradiance on a daily basis. This datacan be used as a basis for determining the baseline illuminationschedule, even if the crops are to be grown in a greenhouse in adifferent geographic region, or indoors in a plant factory. In agreenhouse environment, supplemental electric lighting or motorizedshading devices may be employed as required.

In many situations, the maximum photon flux density incident upon theplant leaf canopy will be less than what the plants would experienceoutdoors under clear skies. Rather than dimming the horticulturalluminaires to emulate hourly cloud cover conditions, therefore, it ismore likely that the plants will be exposed to constant illuminationsufficient to meet their daily light integral requirements.

Critical to the baseline illumination schedule are the sunrise andsunset times, a period of roughly one-half hour wherein thehorticultural luminaires are dimmed from constant daytime illuminationto nighttime. During these periods, the SPD is changed to emulate thetransition in colour from daytime to twilight conditions, and viceversa.

Data representing the desired or optimum daytime SPD, the desired oroptimum twilight SPD, the durations of each, the duration of thetransitions between each, and the changes in SPD during the transitionsare stored in the luminaire controller as the baseline illuminationschedule.

In Step 830, a crop is grown while being subjected to illumination fromthe luminaires in accordance with the illumination schedule.

In Step 840, the crop yield is evaluated in accordance with thepredetermined goals of plant health, growth, flowering, fruit orvegetable quality, and the production of flavonoids, terpenes,medicinally useful plant extracts and other crop-specific criteria. Ifthe goals are not satisfied, the illumination schedule may be varied(Step 850) and Steps 830 and 840 repeated. If the crop is satisfactory,the process ends at Step 860.

Animal Optimization Method

FIG. 9 illustrates an example of the method wherein the scheduling ofthe radiant flux output and SPD of the luminaires is optimized foranimal health, behaviour, and growth on a per-species and per-breedbasis.

In Step 900, an animal species is selected. It is known that differentbreeds of the same animal species may have different environmentalrequirements, and so a particular breed may also have to be selected.

In Step 910, the animal's preferred environmental conditions aredetermined.

In Step 920, a baseline illumination schedule for the selected breed isdetermined based on past industry experience with domestic animals orwildlife observations, where the illumination schedule is intended forthe animals selected breed to attain predetermined growth goals.

Critical to the baseline illumination schedule are the sunrise andsunset times, a period of roughly one-half hour wherein the livestockproduction or aquaculture luminaires are dimmed from constant daytimeillumination to nighttime. During these periods, the SPD is changed toemulate the transition in colour from daytime to twilight conditions,and vice versa.

Data representing the desired or optimum daytime SPD, the desired oroptimum twilight SPD, the durations of each, the duration of thetransitions between each, and the changes in SPD during the transitionsare stored in the luminaire controller as the baseline illuminationschedule.

In Step 930, the animals are raised while being subjected toillumination from the luminaires in accordance with the illuminationschedule.

In Step 940, the animals' health, behaviour, and marketability isevaluated in accordance with the predetermined goals. If the goals arenot satisfied, the illumination schedule may be varied (Step 950) andSteps 930 and 940 repeated. If the goals have been satisfied, theprocess ends at Step 960.

Referring to FIG. 10, a flowchart of an exemplary process is seen forthe operation of a system 500. In Step 1010, the luminaires 530 areoriented above the plants, so that they provide illumination at least ina downwards direction onto the plants. In Step 1020, the luminaires areconnected to the luminaire controller 550. In Step 1030, the luminairesilluminate the plants with a first SPD, for example an SPD that emulatesdaylight. In Step 1040, the controller sends signals to the luminairesso that the illumination that they are providing transitions from thefirst SPD to a second SPD, for example an SPD that emulates twilight.This process is also applicable to the system 700 for controllingluminaires 730. A similar process can be used to control the luminaires760.

Referring to FIG. 11, a flowchart of an exemplary process is seen forthe operation of a system 600. In Step 1110, the luminaires 630 areoriented above the plants, so that they provide illumination at least ina downwards direction onto the plants. Step 1120, further luminaires 660are oriented to the side of the plants, so that they provideillumination at least in a sideways direction onto the plants. In Step1130, the luminaires are connected to the luminaire controller 650. InStep 1140, the luminaires illuminate the plants with an SPD having afirst spatial distribution, for example a spatially varying SPD thatemulates daylight. In Step 1150, the controller sends signals to theluminaires so that the illumination that they are providing transitionsfrom the first spatial distribution to a second spatial distribution,for example a spatially varying SPD that emulates twilight.

In both plant and animal optimization methods, the quantity of data thatmust be evaluated to determine crop yield or animal health, particularlyif the number of input signals from the sensors results in amultidimensional optimization problem for data fusion, may be confusingif not overwhelming. In such situations, it may be necessary to employartificial intelligence techniques using deep learning architectures todiscover hidden patterns that inform changes to the illuminationschedule.

The configurations and/or approaches described herein are exemplary innature, and specific implementations or examples are not to beconsidered in a limiting sense, because numerous variations arepossible. The specific methods or processes described herein mayrepresent one or more of any number of processing strategies. As such,various acts illustrated may be performed in the sequence illustrated,in other sequences, in parallel, or in some cases omitted. Likewise, theorder of the above-described processes may be changed. The subjectmatter of the present disclosure includes all novel and nonobviouscombinations and subcombinations of the various methods, processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

The embodiments of the invention may be varied in many ways. Suchvariations are not to be regarded as a departure from the scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended to be included within the scope of the claims.

The invention claimed is:
 1. An illumination system for a plantcomprising: a luminaire; a controller that provides electrical power tothe luminaire; a growth medium in which roots of the plant grow; and afiber-optic mesh in the growth medium; wherein light from the luminaireis directed into the fiber-optic mesh, which comprises strands that emitthe light along their length into the growth medium; wherein the lightis provided via the growth medium to the roots and directs growth of theroots.
 2. The illumination system of claim 1, wherein the growth mediumis a substrate.
 3. The illumination system of claim 1, wherein thefiber-optic mesh is horizontal.
 4. The illumination system of claim 1,comprising a second fiber-optic mesh in the growth medium and a secondluminaire, the second fiber-optic mesh being illuminated by the secondluminaire.
 5. The illumination system of claim 4, wherein the luminaireand the second luminaire have independently controlled spectral powerdistributions.
 6. The illumination system of claim 4, wherein the growthof the roots is directed towards and through the fiber-optic mesh andthe second fiber-optic mesh.
 7. The illumination system of claim 4,wherein the fiber-optic mesh stimulates positive phototropism in theroots and the second fiber-optic mesh stimulates negative phototropismin the roots.
 8. The illumination system of claim 7, wherein: theluminaire emits red light, far-red light, near-infrared light or anycombination selected therefrom; and the second luminaire emits bluelight, ultraviolet light or both blue light and ultraviolet light. 9.The illumination system of claim 8, wherein: the luminaire emits redlight; and the second luminaire emits blue light.
 10. The illuminationsystem of claim 1, wherein: the luminaire has an adjustable spectralpower distribution (SPD) and an adjustable photon flux output; and thecontroller provides control signals to the luminaire to control the SPDand the photon flux output.
 11. The illumination system of claim 1,wherein the growth medium is transparent.
 12. The illumination system ofclaim 1, forming part of an aeroponic growth system for the plant. 13.The illumination system of claim 1, forming part of a hydroponic growthsystem for the plant.
 14. The illumination system of claim 1, comprisinga further luminaire oriented to deliver further light towards a canopyof the plant and having an adjustable spectral power distribution (SPD)and an adjustable photon flux output; wherein the controller provideselectrical power and control signals to the further luminaire; whereinthe control signals automatically transition the SPD gradually between afirst SPD and a second SPD twice per day while adjusting the photon fluxoutput; wherein the transitions in the SPD and the adjustments to thephoton flux output correspond to changes in illumination that entrain abiological rhythm in the plant.
 15. A method for directing growth of aplant's roots comprising the steps of: providing a growth medium inwhich the roots grow; connecting a controller to a luminaire so that thecontroller provides electrical power to the luminaire; directing lightfrom the luminaire into a fiber-optic mesh in the growth medium, thefiber-optic mesh comprising strands that emit the light along theirlength into the growth medium; wherein the light directs growth of theroots.
 16. The method of claim 15, comprising controlling the luminaireto: emit red light, far-red light, near-infrared light or anycombination selected therefrom to direct the growth of the roots bypositive phototropism; or emit blue light, ultraviolet light or bothblue light and ultraviolet light to direct the growth of the roots bynegative phototropism.
 17. The method of claim 15, comprising: providingone or more further luminaires, each of the further luminaires directingfurther light into a different further fiber-optic mesh in the growthmedium, each further fiber-optic mesh comprising strands that emit thefurther light along their length into the growth medium; wherein theluminaire and the one or more further luminaires all have independentlycontrolled spectral power distributions.
 18. The method of claim 17,comprising directing the growth of the roots towards and through thefiber-optic mesh and each further fiber-optic mesh.
 19. The method ofclaim 15, comprising: orienting a further luminaire to deliver furtherlight towards a canopy of the plant, the further luminaire having anadjustable spectral power distribution (SPD) and an adjustable photonflux output; and providing, from the controller, electrical power andcontrol signals to the further luminaire; wherein the control signalsautomatically transition the SPD gradually between a first SPD and asecond SPD twice per day while adjusting the photon flux output; whereinthe transitions in the SPD and the adjustments to the photon flux outputcorrespond to changes in illumination that entrain a biological rhythmin the plant.
 20. An illumination system for a plant comprising: aluminaire that has an adjustable spectral power distribution (SPD) andan adjustable photon flux output; a controller that provides electricalpower and control signals to the luminaire to control the SPD and thephoton flux output; and a growth medium in which roots of the plantgrow; wherein the light is provided via the growth medium to the rootsand directs growth of the roots.
 21. An illumination system for a plantcomprising: a luminaire; a growth medium in which roots of the plantgrow, the growth medium being illuminated by light from the luminaire; afurther luminaire oriented to deliver further light towards a canopy ofthe plant and having an adjustable spectral power distribution (SPD) andan adjustable photon flux output; a controller that provides electricalpower to the luminaire, and electrical power and control signals to thefurther luminaire; wherein the control signals automatically transitionthe SPD gradually between a first SPD and a second SPD twice per daywhile adjusting the photon flux output; wherein the transitions in theSPD and the adjustments to the photon flux output correspond to changesin illumination that entrain a biological rhythm in the plant; whereinthe light is provided via the growth medium to the roots and directsgrowth of the roots.